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MCAT Nucleic Acids, DNA, and RNA > DNA replication > Flashcards

DNA replication Flashcards

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1
Q

Why is DNA replication considered semiconservative?

A

because when the cell replicates, each cell will contain one strand of DNA from the original cell, while the second strand of DNA will be a new, replicated strand

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2
Q

In which direction does DNA replication occur?

A

5’ to 3’ direction

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3
Q

What is the origin of replication?

A
  • the sequence that signals where replication should start

- prokaryotes have one origin of replication, while eukaryotes have multiple

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4
Q

What is the enzyme that comes to the origin of replication and starts unwinding the DNA?

A

helicase

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5
Q

What is the enzyme that prevents the closure of the DNA molecule once it is unwound by helicase?

A

single stranded binding proteins (SSBP’s)

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6
Q

Which enzyme prevents supercoiling downstream as the helicase is unwinding the DNA?

A

topoisomerase-it cuts and relaxes the DNA to prevent supercoiling

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7
Q

Which enzyme starts at the origin of replication sequence and lays the RNA primer in the 5’ to 3’ direction?

A

primases

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8
Q

Which enzymes is able to bind to the RNA primer and start synthesizing DNA?

A

DNA polymerase

-it also proofreads and removes RNA primer

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9
Q

What is DNA polymerase?

A

the enzyme that binds to the RNA primer and starts synthesizing DNA. It also has ability to proofread and remove the RNA primer

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10
Q

What is helicase

A

unwinds DNA so it can be replicated

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11
Q

What is the leading strand?

A

refers to the strand that is synthesized continuously into the widening of the replication fork

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12
Q

What is the lagging strand?

A

refers to the strand that is not synthesized continuously because it must wait for the replication fork to widen before beginning to polymerize

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13
Q

What are Okazaki fragments

A

The lagging strand fragments that contain both RNA and DNA

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14
Q

What enzyme linkes Okazaki fragments together after the RNA primer is removed?

A

DNA ligase

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15
Q

What is theta replication?

A

refers to prokaryotic DNA replication; as the circular DNA is replicated, one original chromosome strand falls off from the other (which creates an image that looks like the greek letter theta)

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16
Q

What are the 2 prominent DNA polymerases involved in prokaryotic DNA replication?

A

DNA Polymerase I & DNA Polymerase III

17
Q

In prokaryotes, what are the functions of DNA Polymerase III?

A
  • this is the main replicating enzyme; it synthesizes DNA with high processivity and accuracy (is a fast 5’ to 3’ polymerase)
  • it takes over for DNA Pol 1 ~400bp downstream from the ORI sequence.
  • is a 3’ to 5’ exonuclease (the proofreading ability; is able to read the last base it filled in to ensure it is correct. If the last base filled in is not correct, it will replace it with the correct base)
  • has no known function in DNA repair
18
Q

In prokaryotes, what are the functions of DNA Polymerase I?

A
  • This starts adding nucleotides at the RNA primer (5’ to 3’ polymerase); also has 5’ to 3’ exonuclease activity so it can remove the RNA primer and replace it with DNA in 5’ to 3’ activity.
  • This is the “backup” for DNA Polymerase III; has low processivity and therefore is a slow 5’ to 3’ polymerase
  • is a 3’ to 5’ exonuclease (the proofreading ability; is able to read the last base it filled in to ensure it is correct. If the last base filled in is not correct, it will replace it with the correct base)
  • functions in DNA excision repair
19
Q

In prokaryotes, what are the functions of DNA Polymerase II?

A
  • 5’ to 3’ polymerase (functions as a DNA Polymerase III backup)
  • 3’ to 5’ exonuclease
  • has a function in DNA repair pathways
20
Q

In prokaryotes, what are the functions of DNA Polymerase IV & V?

A
  • main function is in DNA repair: play an important part of the prokaryotic checkpoint pathway, as they function to stall other polymerase enzymes at replication forks when the DNA repair pathway has been activated
  • these are error prone in 5’ to 3’ polymerase activity
21
Q

In eukaryotes, DNA polymerases are complex ______ enzymes

A

multisubunit

22
Q

Eukaryotic DNA polymerases has a subunit that works as a ______, and also a subunit that works as a ______

A

polymerase, primase

23
Q

When helicase unwinds the DNA for replication, the open strands are referred to as an ____complex

A

open

24
Q

What is the role of primase in DNA replication?

A

an RNA polymerase that lays down the RNA primer on the template strand

25
Q

In what direction is the template strand read?

A

If the daughter strand is made 5’ to 3’, and the 2 strands have to end up antiparallel, the template strand must be read in the 3’ to 5’ direction

26
Q

The thermodynamic driving force for the polymerization reaction is the removal and hydrolysis of the _____ from each dNTP added to the chain

A

pyrophosphate (P2O7^4-)

27
Q

During replication, both template strands are read in the __1___ direction while the daughter strands are elongated in the ___2___ direction

A

1) 3’ to 5’

2) 5’ to 3’

28
Q

Replication forks grow away from the ____ in both directions

A

origin

29
Q

Each replication fork contains a _____ and _____ strand

A

leading and lagging strand

30
Q

Replication of the leading strand is ___1___ and leads into the replication fork, while the replication of the lagging strand is ___2___, resulting in Okazaki fragments

A

1) continuous

2) discontinuous

31
Q

What is the main role of telomerase?

A

elongates the telomeres on the parental DNA strand

32
Q

Telomerase is a ribonucleoprotein complex, containing a ____ primer and ____ _____ enzyme

A

RNA primer

reverse transcriptase enzyme

33
Q

Telomerase has reverse transcriptase activity because it is able to read it’s __1__ template to generate __2___

A

1) RNA

2) DNA

34
Q

which cells have the innate ability to express telomerase? (4)

A

fetal cells, stem cells (embryonic or adult), spermatogonia, and cancer cells

MCAT Nucleic Acids, DNA, and RNA (5 decks)

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